1. Field of the Invention
The present invention relates to a precipitation hardened copper alloy, and more particularly, to a Cu—Ni—Si alloy suitable for the use in various components of electronic equipment.
2. Description of the Related Art
Copper alloys for electronic materials used in various components of electronic equipment such as lead frames, connectors, pins, terminals, relays, and switches are required to achieve a balance between high strength and high electrical conductivity (or thermal conductivity) as basic characteristics. In recent years, high integration, miniaturization and thickness reduction of electronic components are in rapid progress, and in this respect, a demand for a copper alloy to be used in the components of electronic equipment is rising to higher levels.
From the viewpoints of high strength and high electrical conductivity, the amount of use of precipitation hardened copper alloys is increasing in replacement of conventional solid solution hardened copper alloys represented by phosphor bronze and brass, as copper alloys for electronic materials. In a precipitation hardened copper alloy, as a supersaturated solid solution that has been solution-hot-treated is subjected to an aging treatment, fine precipitates are uniformly dispersed, so that the strength of the alloy increases, the amount of solid-solution elements in copper decreases, and also, electrical conductivity increases. For this reason, a material having excellent mechanical properties such as strength and spring properties, and having satisfactory electrical conductivity and thermal conductivity is obtained.
Among precipitation hardened copper alloys, Cu—Ni—Si copper alloys, which are generally referred to as Corson alloys, are representative copper alloys having relatively high electrical conductivity, strength, stress relaxation characteristic, and bending workability in combination, and constitute one class of alloys for which active development is currently underway in the industry. In this class of copper alloys, an enhancement of strength and electrical conductivity can be promoted by precipitating fine Ni—Si intermetallic compound particles in a copper matrix.
It has been known that the precipitation state of Ni—Si compound particles influences on the alloy characteristics.
Japanese Patent No. 3797736 (Patent Document 1) describes an invention including particles of Ni—Si compound particles with the particle size of equal to or greater than 0.003 μm and smaller than 0.03 μm (small particles), and particles with the particle size of 0.03 μm to 100 μm (large particles) and the ratio between the numbers of small particles and large particles is 1.5 or greater. In addition, the small particles with the particle size of smaller than 0.03 μm increase strength and heat resistance alloy, but rarely contribute to shear workability. Meanwhile, the large particles with the particle size of 0.03 μm or greater rarely contribute to an increase in strength and heat resistance of the alloy, but intensively receive stress at the time of a shear process, become sources of microcrack, and significantly increase the shear workability. In addition, it is mentioned that the copper alloy described in Japanese Patent No. 3797736 has significant shear workability together with strength and heat resistance required as copper alloy for electric and electronic component.
Japanese Patent No. 3797736 describes a method of producing copper alloy as follows.
1) Since grains are especially likely to be coarse if Ni content is 4 wt % or greater and Si content is 1 wt % or greater, molten metal after addition of Ni and Si is maintained at the temperature of 1300° C. or greater (or 5 minutes or greater, both are completely melted, and a cooling rate in a mold from a casting temperature to a solidifying temperature is 0.3° C./second or greater, in order to control measurements of grains into a desired scope.
2) Heat material after hot rolling is subjected to rapid cooling under water, and the material further subjected to cold rolling is heated at 500 to 700° C. for 1 minute to 2 hours to precipitate large particles. After that, the material is additionally subjected to cold rolling, and heated at 300 to 600° C. for 30 minutes or greater to precipitate small particles at this time.
3) Without performing rapid cooling at the time of cooling if hot rolling finishes, the material is maintained at 500 to 700° C. for 1 minute to 2 hours to precipitate large particles, and then subjected to rapid cooling. After the material is further subjected to cold rolling, the material is heated at 300 to 600° C. for 30 minutes or greater to precipitate small particles at this time.
In view of particle sizes of Ni—Si precipitates and other precipitates in the composition of copper alloy, and a relation between a ratio of distribution density and prevention of grains front being coarse, Japanese Patent No. 3977376 (Patent Document 2) describes precipitates X made from Ni and Si, and precipitates V that do not contain one or both of Ni and Si, and describes that a particle size of the precipitates X is 0.001 to 0.1 μm, and a particle size of the precipitates Y is 0.01 to 1 μm. In addition, in order to achieve compatibility between strength and bending workability, it is described that the number of the precipitates X is 30 to 2000 times of the number of the precipitates Y, and the number of the precipitates X is 108 to 1012 per 1 mm2, and the number of the precipitates Y is 104 to 108 per 1 mm2.
Japanese Patent No. 3977376 describes a method of producing the copper alloy as follows.
If an ingot is subjected to hot rolling, the ingot is heated at the heating rate of 20 to 200° C./hour, subjected to hot rolling at 850 to 5050° C. for 0.5 to 5 hours, and subjected to rapid cooling so that the finishing temperature of the hot rolling is 300 to 700° C. Accordingly, the precipitates X and Y are generated. After the hot rolling, a desired plate thickness is obtained by combining, for example, solution treatment, annealing, and cold rolling.
The purpose of the solution treatment is to solid-solubilize Ni and Si precipitated at the time of casting and heating treatment again, and to perform recrystallization at the same time. The temperature of the solution treatment is adjusted according to the added amount of Ni. For example, the temperature is adjusted to 650° C. if the Ni amount is equal to or greater than 2.0 and less than 2.5% by mass, to 800° C. if the Ni amount is equal to or greater than 2.5 and less than 3.0% by mass, to 850° C. if the Ni amount is equal to or greater than 3.0 and less than 3.5% by mass, to 900° C. if the Ni amount is equal to or greater than 3.5 and less than 4.0% by mass, to 950° C. if the Ni amount is equal to or greater than 4.0 and less than 4.5% by mass, and to 980° C. if the Ni amount is equal to or greater than 4.5 and equal to or less than 5.0% by mass.
International Publication No. 2008/032738 (Patent Document 3) describes a copper alloy strip material for electrical electronic equipment which includes a copper alloy, containing 2.0 to 5.0 mass % of Ni, and 0.43 to 1.5 mass % of Si, with the balance being Cu and unavoidable impurities, and in which three types of intermetallic compounds A, B, and C including 50 mass % or greater of Ni and Si in total are contained, the intermetallic compound A has a compound diameter of equal to or greater than 0.3 μm and equal to or less than 2 μm, the intermetallic compound B has a compound diameter of equal to or greater than 0.05 μm and less than 0.3 μm, and the intermetallic compound C has a compound diameter of greater than 0.001 μm and less than 0.05 μm.
In addition, disclosed is a method of producing a copper alloy strip material for electrical/electronic equipment including a step of reheating a copper alloy ingot containing 2.0 to 5.0 mass % of Ni and 0.43 to 1.5 mass % of Si with the balance being Cu and unavoidable impurities at 850 to 950° C. for 2 to 10 hours, a step of performing hot rolling the reheated copper alloy ingot for 100 to 500 seconds to obtain a copper alloy strip material, a step of performing rapid cooling the copper alloy strip material subjected to hot rolling to a temperature of 600 to 800° C. and a step of performing an aging heat treatment on the copper alloy strip material subjected to rapid cooling, at 400 to 550° C. for 1 to 4 hours.    Patent document 1: Japanese Patent No. 3707736    Patent document 2: Japanese Patent No. 3977376    Patent document 3: International Publication No. 2008/032738